THE ARCHDUKE (Lexias pardalis) is a fairly common butterfly of the family Nymphalidae. Although not particularly beautiful, this species is interesting to butterfly watchers because it exhibits sexual dimorphism. The male and female of this species look so different that an uninitiated observer may think they are two different species.
      Generally, we would expect some subtle differences between the males and females of butterfly species, such as slight variations in shape, size, colour or wing patterns. Such differences are minor and it would not be difficult to see that they belong to the same species.
      Among some species, however, the differences between the sexes are so striking that they appear to be distinct species. This phenomenon is known as sexual dimorphism. In the early days of scientific exploration and discovery, this dissimilarity had led to instances when the two sexes had been erroneously classified as different species.
      The Archdule is a fairly large butterfly with a wingspan of 8-9cm. The male is obviously smaller than the female and its wings are nearly black above, marked with some faint spots and a broad pale blue border. The female is dark brown above marked with a profusion of light yellow spots.
      During a recent visit to northern Thailand, I saw for the first time a mating pair of the Archduke. It was in an elephant training

camp in Chiang Dao, about 56km north of Chiang Mai city, that I caught the pair in flagranti on a low tree within the camp.
      In nature, it is extremely rare for creatures to mate with species other than their own (to "inter-mate"). So, one can be very certain that two specimens mating in nature belong to the same species no matter how dissimilar they may look.
      I have encountered the Archduke often enough during my rambles (here in Malaysia) to know that it is flightly butterfly which prefers the shade of the forest understorey. But it may venture out into more open ground to feed on the juice of fallen fruits.
      Thailand has about 1,135 species of butterflies and many of them are also found in Malaysia as the two countries have roughly the same type of vegetation and climatic conditions, and also because Peninsular Malaysia and Thailand form one continuous land mass (with the narrow Isthmus of Kra as a corridor).
      Besides butterflies, sexual dimorphism is seen in other insects, also in birds, fishes and other creatures. In the insect world, the “trilobite larva” represents an extreme form of sexual dimorphism. Resembling the trilobites (which are long-extinct marine organisms), these ground-crawling creatures are in fact the females of the tiny net-winged beetles of the family Lycidae.
      For more butterfly pictures and stories, please visit Chin’s Butterfly Gallery.